The present invention relates in general to technologies for monitoring scenes to be monitored as captured or photographed by cameras in the events of surveillance in road transportation monitoring fields and private surveillance within buildings plus outdoor surveillance or the like. More particularly, but not exclusively, this invention relates to a method and apparatus for monitoring of images to detect abnormalities through image processing of image data of scenes being monitored. The invention also relates to storage media for storing therein computer programs used to realize the image monitoring methodology.
As prior known image monitoring or surveillance apparatus, there is a method for performing abnormality detection through the steps of coding an image as captured or “photographed” by a camera into compressed data involving with-time differential image components and then directly utilizing such with-time differential images in this compressed data with no extra modifications added thereto to thereby determine or “judge” whether a change occurs in the to-be-monitored image (Japanese Patent Application Laid-open No. 2000-20857).
Unfortunately this method is encountered with a problem that under the circumstances with luminance variations with time such as brightness changes due to flickering of fluorescent lamps and/or turn-on/off of illumination devices and daylight variation of sunlight and clouds or the like, these can be detected as abnormalities incorrectly. In addition, due to the fact that tree swing with regular vibration in a direction of movement or alternatively curtain movements or else causes the luminance to change with time, the use of this method would result in incorrect detection of them as abnormalities in some cases.
Another abnormality detection method has been proposed until today, which includes the steps of subdividing an image as photographed by a camera into a plurality of blocks, applying discrete cosine transformation and compression processing to a respective of such blocks for forward transmission, expanding only high-frequency components containing therein edge information of the compressed image thus transferred, and using a difference between it and a prestored background scene image to perform the intended abnormality detection (JP-A-8-50649).
This method, however, suffers from problems which follow: The need for extension or “decompression” of such once-compressed image results in an unwanted increase in image information when compared to the case of compression; the resultant costs can increase undesirably due to an increase in length of time required for execution of the intended processing and also the necessity to employ an extra expansion device. A further problem faced with the prior art method is that detection accuracy stays lower. This can be said because the method tends to incorrectly detect the inherently non-abnormal objects—such as tree swing with regular vibration in movement direction, curtain movement, or else—as abnormal objects due to the fact that these exhibit changes in comparison with the background scene image thereof.